Image and ireport

I use ireport with Access base.
A field of my table, is defined like java.lang.Object, and a .jpg is stored.
I can see this picture with access.
But i would like see it on iReport.
So when i put this field (java.lang.Object) on my report with drag and drop. i can see the first characters, and no "picture".
When i define an Image, with expression class string, i have a compilation error

Caused by: java.lang.ClassCastException: [B cannot be cast to java.lang.String

I can't see what i do ..
please help....

Think

Merci